1. Field of the Invention
This invention relates to an improved method for determining the necessity to chemically clean a granular medium filter bed.
2. Information Disclosure Statement
Granular medium bed filters often experience problems in filtering wastewaters containing greases and oils, or other deleterious materials, which coat the granular medium particles. These substances cause agglomeration of medium particles and retard the passage of liquid through the granular medium bed filters.
Various methods to clean the filter medium are known. In U.S. Pat. No. 3,932,278, Meidl et al. disclose cleaning sand or multi-medium filters with water containing high concentrations of chlorine or ozone.
In U.S. Pat. No. 4,032,443, Ross discloses removal of grease and oil from particulate bed granules by backwashing with a detergent.
U.S. Pat. No. 4,617,131 of Walker and U.S. Pat. No. 4,764,288 of Walker et al., disclose methods of backwashing and purging a filter bed to remove contaminants from the filter bed.
Regardless of how effective the cleaning method may be, if the cleaning cycle is not performed regularly, the granular medium of the filter bed can form "grease balls" or "mud balls" which are difficult to disperse. Unless cleaning is effective and regular, the granular medium of the filter bed may eventually cement together such that chemical cleaning cannot be performed effectively. Replacement of the dirty granular medium may even be required.
Thus it is desirable to perform the chemical cleaning cycle on a granular medium filter on a regular basis to prevent these problems from occurring. Conversely, it is unwise to expend excessive cleaner by cleaning the filter bed unnecessarily if not required for good filter performance. Excessive cleaning also reduces effective filtration time since the filter is off line during cleaning. Consequently, it is desirable to chemically clean a granular medium filter only when performance indicates that cleaning is necessary.